The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
Some forms of electric heaters generally include a substrate, a resistive heating element embedded within or disposed proximate the substrate, and a protective layer disposed over the resistive heating element. The resistive heating element is commonly terminated in a pair of terminal pads, which are not covered by the protective layer, for connecting a pair of lead wires extending from a power source. The connection between the terminal pads and the lead wires is generally insulated from the outside environment to prevent against accidental discharge of the voltage applied by the power source. Conventional termination structures, however, often include numerous parts that define interfaces with enclosed air gaps. Air gaps pose serious arcing problems, particularly when the electric heater is used in a semiconductor manufacturing process, where a relatively high voltage is applied in a vacuum environment.
Generally, arcing is a result of an electrical breakdown that occurs when a voltage applied across an air gap exceeds a threshold breakdown field for the air. Under this high electric field, free electrons in the air gap produce ionizing collisions with air molecules, and thus the air gap becomes an electric current path in addition to a designated electric current path within a conductive element. Unfortunately, arcing often damages the insulation of the termination structure and may lead to malfunction of the termination structure and the overall heater.
Arcing from electrical terminations across an air gap to a conductive surface typically occurs when the electric heater is operated above 340 peak voltage and is dependent upon both the molecular density of the air and the span of the air gap over which the voltage gradient exists. Because the breakdown voltage for a typical air gap in a vacuum chamber initially decreases as the air pressure is reduced below 1 atmosphere, arcing is thus more likely to occur to or from a terminal of an energized heater during evacuation or filling. The conventional termination structure for an electric heater has proven to be especially susceptible to arcing in this vacuum environment, for example, when the electric heater is used in a semiconductor manufacturing process.